1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus, an ultrasonic image processing apparatus, and an ultrasonic image processing method of transmitting an ultrasonic wave to the inside of a tested body and obtaining diagnostic information inside the tested body on the basis of a reflected wave from the inside of the tested body. In particular, the present invention relates to removing of a speckle included in image data.
2. Description of the Related Art
The ultrasonic diagnosis makes it possible that the pulsation of the heart or the movement of an embryo is displayed in real time by a simple operation of bringing an ultrasonic probe into contact with a body surface. In addition, since the ultrasonic diagnosis is very safe, the test may be repeatedly performed. In addition, the system size is small compared with other diagnostic apparatuses, such as an X ray, a CT, and an MRI, and a test at the bedside can also be easily performed. For this reason, it can be said that the ultrasonic diagnosis is an easy diagnostic method. An ultrasonic diagnostic apparatus used in the ultrasonic diagnosis changes in various ways with the type of a function that the ultrasonic diagnostic apparatus has. As a small ultrasonic diagnostic apparatus, an ultrasonic diagnostic apparatus that is so small as to be carried with one hand is being developed. In addition, since the ultrasonic diagnosis does not cause radioactive exposure unlike the X ray, the ultrasonic diagnosis may also be used in an obstetric treatment, a remote medical treatment, and the like. In addition, a recent ultrasonic diagnostic apparatus may collect three-dimensional biological information (volume data) by spatially scanning the inside of the tested body using an ultrasonic probe with a two-dimensional array in which ultrasonic vibrators are arrayed in a two-dimensional manner.
However, received signals from a plurality of adjacent tissues of a tested body interfere with each other due to a phase difference thereof. In addition, an image pattern differently viewed, from that in the case of mixing only amplitude information, that is, a speckle is generated. Since this speckle interferes with correctly observing the position and shape of a boundary of tissues of the tested body, various kinds of processing methods for removing the speckle have been proposed.
As one of the methods, there is a method of performing multiresolution decomposition of an object image by wavelet transform/inverse wavelet transform and performing processing for applying a threshold value, weighting, and the like to a high-frequency component of an image decomposed at each level. Although a speckle is removed in this method, there is a problem that an obtained image depends on artificial sensibility.
Accordingly, for example, JP-A-2006-116307 proposes a method of detecting an edge of an image decomposed at each level, calculating the direction of the edge for every pixel, and performing filtering for making the edge smooth in the tangential direction and the edge clear in the normal direction. Also in this case, however, there is a limitation in performance because making the edge smooth and clear is performed by a fixed filter.
On the other hand, a method of removing a speckle by a nonlinear anisotropic diffusion filter has also been proposed like ‘K. Z. Abd-Elmomiem, A. M. Youssef, and Y. M. Kadah, “Real-Time Speckle Reduction and Coherence Enhancement in Ultrasound Imaging via Nonlinear Anisotropic Diffusion”, IEEE transactions on biomedical engineering, vol. 49, NO. 9, Sep. 2002’. However, since the nonlinear anisotropic diffusion filter needs an operation of solving a partial differential equation for calculation, there is a problem that it takes a time for the calculation processing. In addition, although there is an effect of reducing the speckle to some extent with the single nonlinear anisotropic diffusion filter, there is also a problem that the effect is not enough.
In both of the two methods described above, an object to be processed is a two-dimensional ultrasonic image and it is premised that the process is performed after scan conversion processing in which a coordinate system of the image is converted from a transmitting and receiving system to a display system and before display. In this case, a problem occurs, for example, when only a B-mode image of an image displayed by overlapping the B-mode image and a color Doppler image each other. In addition, a recent display system has high-resolution. For this reason, many pixels should be processed for high resolution after scan conversion processing. This makes it difficult to increase the processing speed. In addition, a case in which ultrasonic image data is volume data is not specifically proposed in the known example.